The use of computer-aided manipulating of electronic models that correspond to physical models has become more prevalent as the capabilities of computer processing systems have increased. One such application of this electronic modeling technology is in the dental field in which electronic models are generated that correspond to physical models made from impressions of teeth and gums in a human mouth. Dentists and other dental health professionals have used these physical models for a patient's teeth to study the interaction of the opposing jaws of the patient. In particular, the models may be used before, during, and after a treatment plan is implemented.
One application of this electronic modeling technology is in measuring the shift in position of a patient's left and right mandibular condyles caused by movement of the mandible. The mandibular condyles are the rounded prominences at the end of the mandible used for articulation with the maxilla. For convenience, each condyle may be thought of as defining a point of rotation for the mandible and maxilla. However, the mandible and maxilla do not interact in a strictly hinge-like fashion, rotating about a fixed point. Rather, during jaw articulation, in which the mandible moves with respect to the maxilla, each condyle shifts with respect to its original position and/or the other condyle. Taking this shift in position into account when creating a treatment plan enables the professional to tailor the plan to better suit the actual physical structure and characteristics of the patient.
FIGS. 1a-1b and 2a-2d illustrate various examples of condyle displacement during jaw articulation. Throughout these figures, the labels CR and CL refer to the right and left condyle respectively. The subscript “O” indicates an open mouth position, whereas the subscript “C” indicates a closed mouth position. As these figures show, the positions of each condyle CR, CL can change during jaw articulation. Referring now to FIGS. 1a-1b, one example of condyle displacement during jaw articulation is shown. FIG. 1a illustrates a front view of a patient's jaw in an open mouth position, depicting the left and right condyle positions CRO, CLO. A straight line between the two condyles CR, CL is shown to better illustrate the movement of each condyle in relation to the other. FIG. 1b illustrates a front view of a patient's jaw in a closed mouth position, depicting the left and right condyle positions CRC, CLC. In FIG. 1b, both condyles CR, CL have shifted slightly from their corresponding open mouth positions CRO, CLO.
FIGS. 2a-2d depict other possible examples of condyle displacement during jaw articulation. FIG. 2a depicts a first example E1 in which no displacement occurs during jaw articulation. FIG. 2b depicts another example E2 in which a lateral shift occurs for both condyles CR, CL during jaw articulation. FIG. 2c depicts yet another example E3 in which the left condyle CL shifts drastically with respect to the right condyle CR while the right condyle CR does not shift. FIG. 2d depicts yet another example E4 in which the left condyle CL shifts less drastically in one direction and the right condyle CR shifts less drastically in the opposite direction. However, while neither condyle CR, CL shifts very far between open and closed mouth positions, the resulting total condyle shift between the right condyle CR and the left condyle CL is just as drastic as in FIG. 2c. 
One known method to measure condyle displacement for an individual patient includes a dental or orthodontic professional estimating the movement of each condyle based on a tactile observation of the shift. Another known method includes using a face bow to measure the distance between a condyle and a point on the patient's face while the patient holds her jaw in various positions. As will be appreciated, such methods are prone to error of a user in judging the magnitude or direction of the displacement.
Therefore, there arises a need in the art for a more accurate method, apparatus, and system to measure condyle displacement (i.e., or movement) for a patient.